Electrode and its fabrication method for semiconductor devices, and sputtering target for forming electrode film for semiconductor devices

ABSTRACT

Disclosed is an electrode for semiconductor devices capable of suppressing the generation of hillocks and reducing the resistivity, which is suitable for an active matrixed liquid crystal display and the like in which a thin film transistor is used; its fabrication method; and a sputtering target for forming the electrode film for semiconductor devices. The electrode for semiconductor devices is made of an Al alloy containing the one or more alloying elements selected from Fe, Co, Ni, Ru, Rh and Ir, in a total amount from 0.1 to 10 At %, or one or more alloying elements selected from rare earth elements, in a total amount from 0.05 to 15 at %. The method of fabricating an electrode for semiconductor devices, includes the steps of: depositing an Al alloy film, in which the elements mentioned above are dissolved in an Al matrix, on a substrate; and precipitating part of all of the elements dissolved in the Al matrix as intermetallic compounds by annealing the Al alloy film at an annealing temperature ranging from 150 to 400° C.; whereby an electrode for semiconductor devices which is made of an Al alloy film with an electrical resistivity lower than 20 μΩcm is obtained. The target is made of an Al alloy containing the above elements.

This is a Division, of application Ser. No. 08/281,028 filed on Jul. 27,1994 now U.S. Pat. No. 5,514,909.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrode for semiconductor devices,its fabrication method, and a sputtering target for forming an electrodefilm for semiconductor devices, and particularly to an electrode forsemiconductor devices which is suitable for an electrode(interconnections and electrode itself) of an active matrixed liquidcrystal display having a thin film transistor, and its fabricationmethod.

2. Description of the Related Art

A liquid crystal display (hereinafter, referred to as "LCD") isexcellent in thinning, lightening and power-saving compared withconventional displays using a cathode-ray tube, and further it iscapable of obtaining a high resolution image. Furthermore, to improvethe image quality, there is proposed an LCD with a thin film transistor(hereinafter, referred to as "TFT") as a switching element. Here, theTFT means an active element composed of a semiconducting film formed onan insulating substrate such as glass, to which an electrode made of athin metal film (interconnection and electrode itself) is connected. Anelectrode for semiconductor devices is used as part of a TFT, and theterm "electrode" as used herein is intended to refer to bothinterconnections and the electrode itself. In the TFT, theinterconnections and the electrode are electrically connected to eachother.

Various properties are required for an electrode for semiconductordevices used for the LCD mentioned above. In the tendency toward largerdisplay size and higher resolution of LCDS, particularly, the loweringof the resistivity becomes most important for suppressing the delay of asignal. For example, in a color LCD with more than 10-inch largedisplay, the resistivity (electrical resistance) of an electrode forsemiconductor devices is required to be lower than 20 μΩcm.

Refractory metals such as Ta, Mo, Cr and Ti are used as the electrodematerials for LCDs with TFTs (hereinafter referred to as "TFT-LCD").However, the metals have high resistivities in the thin film state;about 180 μΩcm (Ta), about 50 μΩcm (Mo), about 50 μΩcm (Cr), and about80 μΩcm (Ti). The resistivities of all these metals greatly exceeds thevalue of 20 μΩcm. Accordingly, to achieve a larger size and higherresolution of TFT-LCDs, there has been required a new electrode materialfor semiconductor devices having a low resistivity (lower than 20 μΩcm).

The electrode material for semiconductor devices having a lowresistivity may include Au, Cu and Al. Au is difficult to etch, whichproperty is required to form a specified pattern after deposition of thefilm, that is, electrode film, and it is expensive. Cu is poor in itsadhesiveness to substrates and in corrosion resistance. Both metals arenot practical. On the other hand, Al is insufficient in thermalstability, and has a disadvantage in generating fine protrusions calledhillocks on the surface of an electrode film during a heating processafter deposition of the electrode film which is inevitable for the TFTfabrication process. In general, in the TFT-LCD, the electrode filmbecomes the bottom layer, so that when hillocks are generated, it isimpossible to deposit a film thereon.

To suppress the generation of hillocks on an Al electrode film, therehas been adopted a technique wherein the heating is performed after ahigh strength film, such as the refractory metals, is deposited on theAl electrode film. However, in this technique, films with differentetching properties must be simultaneously etched, so that it becomesdifficult to obtain a good interconnection pattern. Accordingly, therehas been required an electrode material for semiconductor devices usedfor TFT-LCDs capable of suppressing the generation of hillocks andreducing the resistivity (lower than 20 μΩcm).

Although the present state (prior art, problem and requirement) of anelectrode for semiconductor devices of TFT-LCDs has been described, theelectrode for semiconductor devices is used not only for the TFT-LCD,but also for the electrode and interconnections of an Si semiconductorrepresented by a Large Scale Integrated Circuit (hereinafter referred toas "LSI"). Problems in the electrode used for the LSI is the same asthat of the TFT-LCD. Accordingly, there has also been required anelectrode material for semiconductor devices used for LSIs capable ofsuppressing the generation of hillocks and reducing the resistivity(lower than 20 μΩcm).

SUMMARY OF THE INVENTION

A purpose of the present invention is to provide an electrode forsemiconductor devices with less tendency to generate hillocks and has aresistivity lower than 20 μΩcm. Another purpose of the present inventionis to provide a method of fabricating the electrode for semiconductordevices mentioned above and a sputtering target for forming theelectrode film for semiconductor devices.

The goal mentioned above can be achieved by provision of an electrodefor semiconductor devices, its fabrication method, and a sputteringtarget for forming an electrode film for semiconductor devices.

According to one embodiment of the invention, an electrode forsemiconductor devices is made of an Al alloy containing one or morealloying elements selected from Fe, Co, Ni, Ru, Rh and Ir in a totalamount from 0.1 to 10 at %. According to a second embodiment of theinvention, an electrode for semiconductor devices is made of an Al alloycontaining one or more alloying elements selected from rare earthelements in a total amount from 0.05 to 15 at %.

According to a third embodiment of the invention, an electrode forsemiconductor devices according to the first or second embodiments ofthe invention is formed by a sputtering process. According to a fourthembodiment of the invention, an electrode for semiconductor devicesaccording to the first or second embodiment of the invention is used asan electrode for semiconductor devices in a liquid crystal display.According to a fifth embodiment of the invention, in an electrode forsemiconductor devices according to any of the first four embodiments,the electric resistance of the Al alloy is adjusted to be lower than 20μΩcm by precipitating part or all of the alloying elements dissolved inthe Al matrix as intermetallic compounds.

According to a sixth embodiment of the invention, a method offabricating an electrode for semiconductor devices, includes the stepsof: depositing an Al alloy film, in which one or more alloying elementsselected from Fe, Co, Ni, Ru, Rh and Ir are dissolved in Al matrix, on asubstrate; and precipitating part or all of the elements dissolved inthe Al matrix as intermetallic compounds by annealing the Al alloy filmat an annealing temperature ranging from 150 to 400° C.; whereby anelectrode for semiconductor devices which is made of an Al alloy filmhaving an electrical resistivity lower than 20 μΩcm is obtained.According to a seventh embodiment of the invention, a method offabricating an electrode for semiconductor devices includes the stepsof: depositing an Al alloy film, in which one or more rare earthelements are dissolved in Al matrix, on a substrate; and precipitatingpart or all of the elements dissolved in the Al matrix as intermetalliccompounds by annealing the Al alloy film at a annealing temperatureranging from 150 to 400° C.; whereby an electrode for semiconductordevices which is made of an Al alloy film having an electricalresistivity lower than 20 μΩcm is obtained.

According to an eighth embodiment of the invention, a sputtering targetfor forming an electrode for semiconductor devices, which is used fordepositing an Al alloy film on a substrate according to the sixthembodiment of the invention, is made of an Al alloy containing one ormore alloying elements selected from Fe, Co, Ru, Rh and Ir.

According to a ninth embodiment of the invention, a sputtering targetfor forming an electrode for semiconductor devices, which is used fordepositing an Al alloy film on a substrate according to the seventhembodiment of the invention, is made of an Al alloy containing one ormore rare earth elements.

As used in this application, rare earth elements are intended to includeyttrium (Y), as well as the lanthanoid elements. The lanthanoid elementscontain elements from La, of atomic number 57, to Lu, of atomic number71, in the periodic table.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the relationship between the content of each alloy elementand the resistivity before annealing on Al alloy films for an electrodefor semiconductor devices referring to the first example;

FIG. 2 shows the relationship between the content of each alloy elementand the resistivity after annealing on Al alloy films for an electrodefor semiconductor devices referring to the first example;

FIG. 3 shows the relationship between the annealing temperature and theresistivity on Al alloy films for an electrode for semiconductor devicesreferring to the second example;

FIG. 4 shows the relationship between the content of each alloy elementand the hillock density on Al alloy films for an electrode forsemiconductor devices referring to the third example;

FIG. 5 shows the relationship between the content of each rare earthelement and the resistivity on Al alloy films for an electrode forsemiconductor devices referring to the fourth example;

FIG. 6 shows the relationship between the content of each rare earthelement and the resistivity on Al alloy films for an electrode forsemiconductor devices referring to the fifth example;

FIG. 7 shows the relationship between the annealing temperature and theresistivity on Al alloy films {alloying element: Y, La, Nd} for anelectrode for semiconductor devices referring to the sixth example;

FIG. 8 shows the relationship between the annealing temperature and theresistivity on Al alloy films {alloying element: Gd, Tb, Dy} for anelectrode for semiconductor devices referring to the sixth example; and

FIG. 9 shows the relationship between the annealing temperature and thehillock density on Al alloy films for an electrode for semiconductordevices referring to the seventh example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventors have carried out experiments, in which an Al alloyfilm was deposited by sputtering using a sputtering target of an Alalloy with various added elements, and the compositions and propertiesas an electrode film were examined. From these experiments, the presentinventors have found the following. An Al alloy film containing one ormore elements selected from Fe, Co, Ni, Ru, Rh and Ir (hereinafter,referred to as "Fe, etc."), or one or more rare earth elements(hereinafter, referred to as "REM") has excellent thermal stability, andless tendency to generate hillocks during heating after deposition (thatis, after formation of an electrode film), and further is reduced inresistivity after the heating process. Consequently, the above Al alloyfilm can satisfy the requirements of a high thermal stability (highhillock resistance) and a low resistivity, before and after the heatingprocess (or upon heating). In particular, by positively utilizing theheating process as the heat treatment, and adjusting the annealingtemperature, it becomes possible to obtain an Al alloy film satisfyingthe above requirements by selecting the most suitable heating condition.The present invention is the result of this knowledge.

In an Al alloy film containing Fe, etc. or REM, as the contents of Fe,etc., or REM are larger, the film is greatly reinforced by the so-calledsolid-solution effect of the elements and is thereby improved in thermalstability. As a result, less hillocks on such an Al film are generatedduring heating after deposition (after formation of electrode film).However, such an Al alloy film having improved thermal stability (highhillock resistance) is simultaneously reduced in resistivity by theso-called solid-solution effect. Namely, the Al alloy film does notsatisfy the requirement of specified resistance lower than 20 μΩcm.

However, by annealing the Al alloy film, elements (Fe, etc. or REM)dissolved in an Al matrix are precipitated as intermetallic compounds,so that the total volume of the elements in solid-solution, which causesan increase in resistivity, is reduced, as a result of which theresistivity becomes lower than 20 μΩcm. Therefore, the Al alloy filmcontaining Fe, etc, or REM can satisfy the requirements of a highthermal stability (high hillock resistance) and a low resistivity beforeand after the annealing, after deposition. In particular, by utilizingthe annealing as the heat treatment for positively precipitatingintermetallic compounds, and adjusting the total volume of the elementsdissolved in the Al matrix after the heat-treatment through adjustmentof the annealing temperature, the Al alloy film can satisfy eachrequirement by selecting the most suitable heating condition.

The contents of Fe, etc. are required to be in the range from 0.1 to 10at %. When the contents of Fe, etc. are less than 0.1 at %, the Al alloyfilm is poor in thermal stability because the volume of the elementsdissolved in the Al matrix is small, and it is possible to generatehillocks in the annealing. When the contents of Fe, etc. are more than10 at %, it is difficult to satisfy the requirement of specificresistance lower than 20 μΩcm because the total volume of the elementsdissolved in Al matrix is large, even by adjustment of the total volumeof the elements dissolved in the Al matrix after the annealing(adjustment of the annealing temperature). In addition, when thecontents of Fe, etc. are 5 at % or less, the resistivity becomes lowerthan 20 μΩcm by the usual heating process after deposition of anelectrode film or without heating. In this regard, the content of Fe,etc. is preferably specified to be in the range from 0.1 to 5 at %. Onthe other hand, the contents of REM are required to be in the range from0.05 to 15 at %. The reason for this is the same as the reason describedwith respect to the contents of Fe, etc. When the content of REM is lessthan 0.05 at %, the Al alloy film may generate hillocks; and when theyare more than 15 at %, it is difficult to satisfy the requirement ofresistivity lower than 20 μΩcm.

An electrode for semiconductor devices according to the presentinvention is made of an Al alloy containing Fe, etc. in the total amountfrom 0.1 to 10 at %, or REM in the total amount from 0.05 to 15 at %,and therefore, the electrode is less likely to generate hillocks andsatisfies the requirement of resistivity lower than 20 μΩcm.

The electrode for semiconductor devices according to the presentinvention has such excellent properties, and is suitably used for anelectrode for semiconductor devices in LCDs, equivalent to an Al alloyfilm described in the third embodiment of the invention.

An Al alloy used for an electrode for semiconductor devices according tothe present invention is desirable to be deposited by sputtering. Thereason for this is as follows: Namely, Fe, etc. and REM have extremelysmall solubility limits in Al in the equilibrium state. However, for Alalloy films deposited by sputtering, equivalent to an electrode forsemiconductor devices described in the second embodiment of theinvention, Fe, etc. and REM can be dissolved in solid solution bysputtering (by vapor phase rapid quenching). Accordingly, the Al alloyfilm can be significantly improved in properties such as thermalstability compared with the Al alloy film formed by the other method.

The Al alloy of an electrode for semiconductor devices according to thepresent invention is first deposited by the sputtering mentioned aboveor the like. At this time (that is, in the intermediate state), all orpart of the alloying elements are in the solid-solution state. At thesubsequent heating process or after the annealing (final state), part orall of the alloying elements in the solid-solution state areprecipitated as intermetallic compounds, so that the electricalresistivity is adjusted to be lower than 20 μΩcm, equivalent to anelectrode for semiconductor devices described in the fifth embodiment ofthe invention.

On the other hand, in a method of fabricating an electrode forsemiconductor devices according to the present invention the heatingprocess after film deposition (after formation of an electrode film) ispositively utilized as the heat treatment for precipitatingintermetallic compounds. Namely, an Al alloy film containing Fe, etc. orREM is deposited on a substrate in the state that alloying elements (Fe,etc. or REM) are dissolved in an Al matrix. In this case, as the volumeof the elements dissolved in the Al matrix becomes larger, the Al alloyfilm is more reinforced by the so-called solid-solution effect and isthereby improved in thermal stability, although the resistivity becomehigher. After this film deposition, the heat treatment is applied to theAl alloy film. By this heat treatment, the elements dissolved in the Almatrix are precipitated as intermetallic compounds and the total volumeof the elements in the solid-solution state, which causes an increase inresistivity, is reduced, as a result of which the resistivity isdecreased. Thus, by positively utilizing the heating process after filmdeposition, the Al alloy film can satisfy the requirements of a highthermal stability and a low resistivity (the high thermal stability is arequirement during heating, and the low resistivity is a requirementafter heating).

Accordingly, a method of fabricating an electrode for semiconductordevices includes the steps of: depositing an Al alloy film, in which Fe,etc. or REM are dissolved in an Al matrix, on a substrate; andprecipitating part or all of the elements dissolved in the Al matrix asintermetallic compounds by annealing the Al alloy film at an annealingtemperature ranging from 150 to 400° C.; whereby an electrode forsemiconductor devices which is made of an Al alloy film with anelectrical resistivity lower than 20 μΩcm is obtained. This method is anextremely reasonable process capable of satisfying the requirements of ahigh thermal stability and a low resistivity before and after theheating process (heat treatment).

Here, it may be determined whether or not all of the elements dissolvedin the Al matrix should be precipitated as intermetallic compounds inaccordance with the volume of the elements dissolved in the Al matrixbefore annealing and the desired electrical resistivity. Moreover, whenit is determined that part of them should be precipitated, theprecipitated amount based on the whole volume of the elements dissolvedin the Al matrix is similarly determined. The annealing temperature inthe heat treatment is specified to be in the range from 150 to 400° C.When it is less than 150° C., the intermetallic compounds are notprecipitated, so that the Al alloy film cannot satisfy the requirementof electric resistance lower than 20 μΩcm. When it is more than 400° C.,hillocks are generated during annealing.

In the deposition of the Al alloy film mentioned above by sputtering,there may be used a sputtering target made of an Al alloy containing Fe,etc. or REM. Such an Al alloy target has an advantage in stabilizing thecomposition of the deposited Al alloy film or reducing the oxygen amountcompared with a composite target and the like.

The present invention will be more clearly understood by way ofexamples.

EXAMPLE 1

A binary Al alloy film with a 300 nm thickness was deposited on a glasssubstrate with a 0.5 mm thickness, by DC magnetron sputtering, using acomposite target in which a specified number of {Fe, Co, Ni, Ru, Rh orIr (purity: 99.9% for each element)} chips (5 mm×5 mm) were put on apure Al target (purity: 99.999%), or a vacuum melted Al alloy targetcontaining Fe, etc. in specified amounts. The Al alloy film is used asan interconnection of an electrode for semiconductor devices.

The composition of the films thus obtained was analyzed by ICP, and theresistivity thereof was measured at room temperature by four-point probemethod. The film was then annealed at 400° C. for 1 hr. The resistivityof the film was similarly measured. The results are summarized in therelationship between amount of Fe, etc. (hereinafter, referred to as"content of alloy element") and resistivity, which are shown in FIG. 1(before annealing) and FIG. 2 (after annealing). The resistivity isincreased linearly with increasing the content of an alloying element.However, the resistivity is decreased by the annealing at 400° C., andwhich is lower than 20 μΩcm even when the content of alloying element isincreased up to 10 at %.

EXAMPLE 2

An Al alloy film was formed on a substrate to the same thickness as inExample 1 the same way as in Example 1, using a vacuum melted Al alloytarget of Al-10 at %Fe. The film was annealed at a temperature rangefrom 100 to 500° C. for 1 hr. The resistivity of this film was measuredthe same way as in Example 1. The results are summarized in therelationship between the annealing temperature and the resistivity. Asis apparent from this figure, the resistivity is decreased when theannealing temperature is higher than 150° C.

EXAMPLE 3

An Al alloy film containing one or more alloying elements selected fromFe, Co, Ni, Ru, Rh or Ir was formed the same way as Example 1. The filmwas annealed at 400° C. for 1 hr, and was observed by opticalmicroscopy. The results are summarized in the relationship between thecontent of an alloying element and the hillock density, which are shownin FIG. 4. The hillock resistance is significantly improved by theaddition of Fe, etc.

EXAMPLE 4

A binary Al alloy film with a 300 nm thickness was deposited on a glasssubstrate with a 0.5 mm thickness, by DC magnetron sputtering, using acomposite target in which a specified number of (rare earth elements)chips (5 mm×5 mm) were put on a pure Al target (purity: 99.999%), or avacuum melted Al alloy target containing a rare earth element inspecified amount. The composition of the film was analyzed and theresistivity thereof was measured the same way as in Example 1. Theresults are summarized in the relationship between the content of rareearth element in the film and the resistivity, which are shown in FIG.5. The resistivity is increased linearly with increasing the content ofthe rare earth element. However, when the content of the rare earthelement is 4 at % or less, the resistivity is lower than 20 μΩcm withoutannealing.

EXAMPLE 5

Al alloy film with the same composition as in Example 4 was depositedthe same way as in Example 4. The composition of the film was analyzedthe same way as in Example 1. The film was then annealed at 300 or 500°C. for 1 hr. The resistivity of the film was measured the same way as inExample 1. The results are shown in FIG. 6. The resistivity is increasedlinearly with increasing the content of the rare earth element. Theincreasing rate of the resistivity is 0.1 μΩcm/at % for the film whichis annealed at 300° C., and 0.5 μΩcm/at % for the film which is annealedat 500° C., each of which is significantly small. The resistivity islower than 20 μΩcm even when the content of the rare earth element is 15at. %

EXAMPLE 6

Al alloy film with the same thickness as in Example 4 was deposited thesame way as in Example 4, using a composite target in which a specifiednumber of {Y, La, Nd, Gd, Tb or Dy (rare earth element)} chips (5 mm×5mm) were put on a pure Al target (purity: 99.999%), or a vacuum meltedAl alloy target containing a rare earth element in specified amount. Thecomposition of the film was analyzed and the resistivity thereof wasmeasured the same way as in Example 1. The film was then annealed at atemperature range from 150 to 400° C. for 1 hr. The resistivity of thefilm was similarly measured. The results are summarized in therelationship between the annealing temperature and the resistivity,which are shown in FIG. 7 (alloying element: Y, La, Nd), and in FIG. 8(alloying element: Gd, Td, Dy). The resistivity is reduced by annealingat higher than 150° C. compared with that before the annealing. It isrevealed that the resistivity is lower than 20 μΩcm by the annealing forboth films containing a light rare earth element and heavy rare earthelement.

EXAMPLE 7

An Al alloy film with a composition of Al-1.5 at %Gd was deposited thesame way as in Example 4. The films were patterned with a 10 μm widestripe by photolithography. The film was annealed at a temperature rangefrom 200 to 400° C. for 1 hr, and was observed by optical microscopy.The results are summarized in the relationship between the annealingtemperature and the hillock density (for each length of 100 μm in astripe pattern with a 10 μm width), which are shown in FIG. 9. The filmhas only one or less of the hillock density, even when being annealed ata relatively high temperature of 400° C. As a result, the film issuitable for an electrode for semiconductor devices of LCDs.

In the above-described examples, one of Fe, etc. or REM is added;however, the same effect can be obtained when two or more of Fe, etc. orREM are added.

What is claimed is:
 1. A sputtering target consisting of an alloy of Al and 0.05-15 at % Nd.
 2. The sputtering target of claim 1, containing 0.05-9 at % Nd.
 3. The sputtering target of claim 1, containing 0.05-6 at % Nd.
 4. The sputtering target of claim 1, containing 0.05-4.28 at % Nd.
 5. The sputtering target of claim 1, containing no scandium. 